2:  #include <petsc/private/viewerimpl.h>

  4: /*@C
  5:    PetscViewerGetSubViewer - Creates a new PetscViewer (same type as the old)
  6:     that lives on a subcommunicator

  8:     Collective on PetscViewer

 10:    Input Parameter:
 11: .  viewer - the PetscViewer to be reproduced

 13:    Output Parameter:
 14: .  outviewer - new PetscViewer

 16:    Level: advanced

 18:    Notes:
 19:     The output of the subviewers is synchronized against the original viewer. For example, if a
 20:     viewer on two MPI ranks is decomposed into two subviewers, the output from the first viewer is
 21:     all printed before the output from the second viewer. You must call PetscViewerFlush() after
 22:     the call to PetscViewerRestoreSubViewer().

 24:     Call PetscViewerRestoreSubViewer() to destroy this PetscViewer, NOT PetscViewerDestroy()

 26:      This is most commonly used to view a sequential object that is part of a
 27:     parallel object. For example block Jacobi PC view could use this to obtain a
 28:     PetscViewer that is used with the sequential KSP on one block of the preconditioner.

 30:     Between the calls to PetscViewerGetSubViewer() and PetscViewerRestoreSubViewer() the original
 31:     viewer should not be used

 33:     PETSCVIEWERDRAW and PETSCVIEWERBINARY only support returning a singleton viewer on rank 0,
 34:     all other ranks will return a NULL viewer

 36:   Developer Notes:
 37:     There is currently incomplete error checking that the user does not use the original viewer between the
 38:     the calls to PetscViewerGetSubViewer() and PetscViewerRestoreSubViewer(). If the user does there
 39:     could be errors in the viewing that go undetected or crash the code.

 41:     It would be nice if the call to PetscViewerFlush() was not required and was handled by 
 42:     PetscViewerRestoreSubViewer()

 44: .seealso: PetscViewerSocketOpen(), PetscViewerASCIIOpen(), PetscViewerDrawOpen(), PetscViewerRestoreSubViewer()
 45: @*/
 46: PetscErrorCode  PetscViewerGetSubViewer(PetscViewer viewer,MPI_Comm comm,PetscViewer *outviewer)
 47: {
 49:   PetscMPIInt    size;

 54:   MPI_Comm_size(PetscObjectComm((PetscObject)viewer),&size);
 55:   if (size == 1) {
 56:     PetscObjectReference((PetscObject)viewer);
 57:     *outviewer = viewer;
 58:   } else if (viewer->ops->getsubviewer) {
 59:     (*viewer->ops->getsubviewer)(viewer,comm,outviewer);
 60:   } else SETERRQ1(PETSC_COMM_SELF,PETSC_ERR_SUP,"Cannot get SubViewer PetscViewer for type %s",((PetscObject)viewer)->type_name);
 61:   return(0);
 62: }

 64: /*@C
 65:    PetscViewerRestoreSubViewer - Restores a new PetscViewer obtained with PetscViewerGetSubViewer().

 67:     Collective on PetscViewer

 69:    Input Parameters:
 70: +  viewer - the PetscViewer that was reproduced
 71: -  outviewer - new PetscViewer

 73:    Level: advanced

 75:    Notes:
 76:     Call PetscViewerGetSubViewer() to get this PetscViewer, NOT PetscViewerCreate()

 78: .seealso: PetscViewerSocketOpen(), PetscViewerASCIIOpen(), PetscViewerDrawOpen(), PetscViewerGetSubViewer()
 79: @*/
 80: PetscErrorCode  PetscViewerRestoreSubViewer(PetscViewer viewer,MPI_Comm comm,PetscViewer *outviewer)
 81: {
 83:   PetscMPIInt    size;


 88:   MPI_Comm_size(PetscObjectComm((PetscObject)viewer),&size);
 89:   if (size == 1) {
 90:     PetscObjectDereference((PetscObject)viewer);
 91:     if (outviewer) *outviewer = NULL;
 92:   } else if (viewer->ops->restoresubviewer) {
 93:     (*viewer->ops->restoresubviewer)(viewer,comm,outviewer);
 94:   }
 95:   return(0);
 96: }